In a timing transmission, the transmission medium, typically a chain, is in sliding engagement with a pivoted guide, which serves as a tensioner lever in cooperation with a tensioner, on the slack side of the transmission, and in sliding engagement with a fixed guide on the tension side of the transmission. The guide body is typically made of a primary resin and a sliding-contact portion is made of secondary resin. The sliding-contact portion is fused with and integrated into a supporting portion of the guide body and configured to slidably contact a chain. Japanese laid-open Patent Application No. 2004-150615, discloses a guide formed by two-color molding, wherein the strength of the fusion of the interface between the guide body and the sliding-contact portion is enhanced.
U.S. Pat. No. 7,524,254, granted Apr. 28, 2009, describes another transmission guide in which plural L-shaped engagement pieces engage with the sides of the guide base. Strips protruding from the sides of the guide base engage with cut-away portions of the shoe. The L-shaped protrusions and strips are staggered along the length of the guide in a zigzag formation along the two sides of the guide. This arrangement provides for easier assembly of the guide, prevents the shoe from falling out by engagement of the shoe and the base, and keeps the chain stable without causing detachment of the shoe.
Because automobiles are driven in various climates of the world, chain guides are exposed to a range of temperatures from below freezing to high temperatures such as those in desert regions. The chain guide is also exposed to engine oil at a high temperature. The transmission chain also generates frictional heat as it slides on the sliding-contact portion of the guide. Thus, the chain guide is used under varying temperatures from below freezing to exceeding 100° C., so that a glass fiber reinforced resin composing the guide body and the non-reinforced resin composing the sliding-contact portion expand and contract when the engine is operating, in a manner similar to the manner in which metal components expand and contract with changes in temperature. The degree of expansion and contraction of the non-reinforced resin is greater than the degree of expansion and contraction of a glass fiber-reinforced resin. As a result, when the engine is operated at low temperatures, the sliding-contact portion contracts more than the guide body and is destroyed sooner. Furthermore, when the engine is operated at high temperatures, the sliding-contact portion can detach from, or falls out of, the guide body because the sliding-contact portion expands more than the guide body.
In the prior art guide described in U.S. Pat. No. 7,524,254, because the base frame is molded of glass fiber-reinforced resin and the shoe composed of the non-reinforced resin, the guide must be assembled by engaging, while twisting, the hook portions and the projecting strips provided in the shoe with the cutaway portions provided in the base frame. The guide is also provided with a predetermined gap between the cutaway portion of the base frame and the hook portion of the shoe so that the shoe freely moves in the longitudinal direction to absorb the thermal expansion and contraction of the shoe.
As a result, when the transmission chain vibrates due to fluctuation of load on the engine, the shoe moves back and forth in the longitudinal direction within the gap and the hook portion of the shoe collides with the cutaway portion of the base frame, generating noise. Further, if the back and forth movement increases, the part where the hook portion of the shoe collides against the cutaway portion of the base frame wears, the hook portion can be broken, and the contact surface of the base frame and the shoe can become worn and damaged.